Genomes and Genes

Species

Avoiding toxicity associated with MTP ablation

Summary

Principal Investigator: M Mahmood Hussain

Abstract: DESCRIPTION (provided by applicant): High plasma lipids and lipoproteins are risk factors for various cardiovascular and metabolic disorders. An approach to lower plasma lipids is to inhibit apoB-lipoprotein biosynthesis, a process critically dependent on an endoplasmic reticulum (ER) resident chaperone, microsomal triglyceride transfer protein (MTP). MTP inhibitors decrease apoB-lipoprotein secretion and lower plasma cholesterol. However, they increase plasma aminotransferases, such as ALT and AST, indicating liver injury. We hypothesize that increases in plasma hepatic enzymes associated with MTP inhibition are due to increases in microsomal free cholesterol, induction of ER stress and cell death. We further hypothesize that reducing cellular free cholesterol along with MTP inhibition might reduce hyperlipidemias and avoiding toxicities associated with MTP antagonists. In the first aim, Alb-Cre-MTPfl/fl or MTPfl/fl mice will be fed T-0901317, a LXR agonist to induce free cholesterol efflux;lovastatin, a HMG Co-A reductase antagonist to inhibit cellular cholesterol biosynthesis;or WY14643, a PPAR1 agonist to enhance 2-oxidation of fatty acids, for 3 or 24 weeks. In another group, &-3 fatty acids, PPAR1/4 agonists, will be injected intraperitoneally to reduce hepatic triglyceride and free cholesterol. In addition, Alb-Cre-MTPfl/fl mice will be fed a western diet and then treated with T-0901317, lovastatin, WY14643, or &-3 fatty acids. Experiments will then be performed in C57Bl/6J mice fed a western diet and fed daily with MTP inhibitors. Additionally, they will be fed olive oil alone or with other compounds described above to determine if toxicities associated with MTP inhibitors can be avoided by these treatments. Outcome measurements will involve changes in apoB-lipoproteins and hepatic enzymes in the plasma;hepatic triglycerides, esterified cholesterol, and free cholesterol;quantification of candidate mRNAs and proteins involved in cholesterol and triglyceride biosynthesis, ER stress, as well as AST/ALT isoforms. These studies will show that toxicities associated with MTP inhibition can be avoided by reducing hepatic free cholesterol. The second aim is to test the hypothesis that release of hepatic enzymes in the plasma is due to the induction of the ER stress and apoptosis. We will first demonstrate that MTP inhibition increases microsomal free cholesterol. Second, we will identify the ER stress pathways activated by MTP ablation/inhibition. Third, we will establish that MTP inhibition induces apoptosis. Fourth, a link between the ER stress and induction of apoptosis will be established. Fifth, importance of the ER stress pathways will be substantiated using ATF6-/-, CHOP-/- and Alb-Cre-Ire11fl/fl mice fed MTP inhibitors. Sixth, we will determine if induction of ER stress by tunicamycin increases plasma AST/ALT levels. At the completion of these studies, we will find out molecular mechanisms responsible for unwanted side effects associated with MTP therapy and suggest solutions to avoid these toxicities. These studies may lead to new therapeutic modalities for the treatment of various hyperlipidemias and have immediate potential for translational use. PUBLIC HEALTH RELEVANCE: This proposal is to find out why MTP drugs cause unwanted side effects and to come up with novel solutions to avoid these effects. These studies will explain molecular mechanisms involved in toxicities associated with MTP inhibitors and genetic ablations. Proposed studies may lead to new therapeutic modalities for the treatment of various disorders associated with high plasma lipids.

..High fasting serum lipid levels are significant risk factors for atherosclerosis. However, the contributions of postprandial excursions in serum lipoproteins to atherogenesis are less well-characterized...

Loss of both phospholipid and triglyceride transfer activities of microsomal triglyceride transfer protein in abetalipoproteinemia

Joby JosekuttySchool of Graduate Studies, Molecular and Cell Biology Program, State University of New York Downstate Medical Center, Brooklyn, New York 11203, USAJ Biol Chem 288:14372-83. 2013

..Thus, transcriptional up-regulation of GPT/GOT1 genes is a major mechanism, in response to ER stress, elevating plasma transaminases. Increases in plasma and tissue transaminases might represent a normal response to stress for survival...

..Significance: These studies may ultimately lead to fundamental insights for understanding, treating or preventing the metabolic alterations and declined cognitive and immune function characteristic of elders. ..

..These six Projects will be supported by four cores and together will form a highly interactive and synergistic Program Project that is focused on lipid and lipoprotein metabolism in atherosclerosis. ..